This invention relates generally to heart rate monitors, and, more particularly, to heart rate monitors that adjust for heartbeat artifacts and thus provide more accurate estimates of heartbeat rate.
Heart rate monitors of this general type typically detect the successive heartbeats and measure the time durations between them. Each time duration measurement is converted into a corresponding frequency or rate, and a prescribed number of the most recently occurring measurements are averaged, to produce an estimate of the heartbeat rate. This estimate is updated upon the detection of each new heartbeat.
One drawback of the typical heart rate monitor described above is that heartbeat artifacts can sometimes cause inaccurate estimates of the heartbeat rate to be made. These artifacts can be caused, for example, by physical movement of electrode wires and by switching noise introduced through electrical power lines.
One solution to the problems associated with heartbeat artifacts is presented in U.S. Pat. No. 4,248,244 to Charnitski et al., in which detected beats are assumed to be artifacts if they occur at intervals differing from previous intervals by more than a prescribed percentage. These detected beats are discarded, and the timing for the next detected beat is reinitiated. Although this technique is generally effective in reducing the effects of heartbeat artifacts, it is not believed to be entirely satisfactory. This is because once a determination is made that a particular detected beat is an artifact, the timing information corresponding to it is discarded and thus not available for future use if it is later determined that the detected beat was in fact an actual heartbeat and not an artifact. Undue delay is then incurred before the apparatus once again provides an accurate estimate of heartbeat rate.
It should be appreciated from the foregoing that there is still a need for an effective heart rate monitor having means for reducing the effects of heartbeat artifacts, without introducing an undue time delay in providing an accurate estimate of heartbeat rate when an actual heartbeat is mistakenly assumed to be an artifact. The present invention fulfills this need.